This invention relates to a recording medium and method of producing the same, and more particularly to formation of a protective layer on a recording layer of a recording medium such as magnetic tape, magnetic disc, magnetic card, opto-magnetic disc, optical disc, etc.
The conventional technology is explained by use of a magnetic recording medium as one example. Magnetic recording media are roughly classified into two types, i.e., coating type and deposition type.
The coating type magnetic recording medium is generally formed by the following method. A magnetic powder such as Fe.sub.2 O.sub.3 or .gamma.-Fe.sub.2 O.sub.3 having an additive of CO is mixed with polyvinyl butyral, toluene and methyl isobutyl ketone so that the mixed material becomes coating agent. Then, the coating agent is applied on a surface of a base of the recording medium at 4.about.5 .mu.m thickness. This method has an advantage in that production of the recording medium is easy, but has disadvantages in that performance is not sufficient for use in high density recording since there is a limit to reducing the size of magnetic powder.
In contrast, the deposition type has a better recording density than that of the coating type, but has problem in durability since magnetic metal layer is exposed on the surface of the recording medium. To solve this problem, an overcoating is applied on a deposition metal layer of 1000.about.2000 .ANG. which is formed by use of spattering method or of electron beam, and further, a smoothing agent is applied on the deposition metal layer. However, even this processing can not solve the problem perfectly. That is, sufficient durability can not be obtained. In addition, since overcoating and coating of the smoothing agent of a thinner and even thickness are difficult to carry out, a gap between a recording or reading magnetic head and a recording layer is widened so that it is not difficult to obtain sufficient high density recording performance.